DaimlerChrysler AG's Freightliner heavy-truck unit, facing a loss of about $1 billion this year, is pressuring many of the trucking fleets that buy its rigs to renegotiate sale-repurchase contracts Freightliner contends it can no longer afford.

DaimlerChrysler has acknowledged problems at Freightliner, North America's No. 1 heavy-truck maker, and is expected later this month to announce a major restructuring. But Freightliner's difficulties now appear worse than previously disclosed. Freightliner is on track to post losses...